Accident Report Detail

Executive Summary

Executive Summary

​On Friday, March
23, 2018, about 9:27 a.m., Pacific daylight time, a 2017 Tesla Model X P100D
electric-powered passenger vehicle, occupied by a 38-year-old driver, was
traveling south on US Highway 101 (US-101) in Mountain View, Santa Clara
County, California. As the vehicle approached the US-101/State Highway (SH-85)
interchange, it was traveling in the second lane from the left, which was a high-occupancy-vehicle
(HOV) lane for continued travel on US-101.

According to
performance data downloaded from the vehicle, the driver was using the advanced
driver assistance features traffic-aware cruise control and autosteer lane-keeping
assistance, which Tesla refers to as “autopilot.” As the Tesla approached the paved
gore area dividing the main travel lanes of US-101 from the SH-85 exit ramp, it
moved to the left and entered the gore area.[1]The Tesla continued traveling
through the gore area and struck a previously damaged crash attenuator at a
speed of about 71 mph.[2] The
crash attenuator was located at the end of a concrete median barrier. The speed
limit on this area of roadway is 65 mph. Preliminary recorded data indicate
that the traffic-aware cruise control speed was set to 75 mph at the time of
the crash.[3] The
impact rotated the Tesla counterclockwise and caused a separation of the front portion
of the vehicle. The Tesla was involved in subsequent collisions with two other
vehicles, a 2010 Mazda 3 and a 2017 Audi A4 (see figure 1).

A preliminary review of the
recorded performance data showed the following:

The
Autopilot system was engaged on four separate occasions during the 32-minute trip,
including a continuous operation for the last 18 minutes 55 seconds prior to
the crash.

During
the 18-minute 55-second segment, the vehicle provided two visual alerts and one
auditory alert for the driver to place his hands on the steering wheel. These
alerts were made more than 15 minutes prior to the crash.

During
the 60 seconds prior to the crash, the driver’s hands were detected on the
steering wheel on three separate occasions, for a total of 34 seconds; for the
last 6 seconds prior to the crash, the vehicle did not detect the driver’s
hands on the steering wheel.

At 8
seconds prior to the crash, the Tesla was following a lead vehicle and was traveling
about 65 mph.

At 7
seconds prior to the crash, the Tesla began a left steering movement while
following a lead vehicle.

At 4
seconds prior to the crash, the Tesla was no longer following a lead vehicle.

At 3
seconds prior to the crash and up to the time of impact with the crash attenuator,
the Tesla’s speed increased from 62 to 70.8 mph, with no precrash braking or
evasive steering movement detected.

During the
collision sequence, the Tesla’s 400-volt lithium-ion high-voltage battery was
breached, and a postcrash fire ensued (see figure 2). The driver was found
belted in his seat. Bystanders removed him from the vehicle before it was
engulfed in fire. The driver was transported to a local hospital, where he died
from his injuries. The driver of the Mazda sustained minor injuries, and the driver
of the Audi was uninjured.​

The Mountain View Fire
Department applied approximately 200 gallons of water and foam during a period
of fewer than 10 minutes to extinguish fires involving the vehicle interior and
the exposed portion of the high-voltage battery. Technical experts from Tesla
responded to the scene to assist in assessing high-voltage hazards and fire
safety. After being allowed to cool, the vehicle was transported with a fire
engine escort to an impound lot in San Mateo. The highway was reopened at 3:09
p.m.

Around 4:30 p.m. that
afternoon, at the impound lot, the Tesla battery emanated smoke and audible
venting. The battery was monitored with a thermal imaging camera, but no active
fire operations were conducted. On March 28, 5 days after the crash, the battery
reignited. The San Mateo Fire Department responded and extinguished the fire.

The crash attenuator was an SCI smart cushion
attenuator system, which was previously damaged on March 12, 2018, in a single-vehicle
crash involving a 2010 Toyota Prius (see figure 3).​

The NTSB continues to work with the
California Highway Patrol and the California Department of Transportationto collect
and analyze data, including all pertinent information relating to the vehicle
operations and roadway configuration. All aspects of the crash remain under
investigation as the NTSB determines the probable cause, with the intent of
issuing safety recommendations to prevent similar crashes.​

[1]A gore area is a triangular-shaped boundary
created by white lines marking an area of pavement formed by the convergence or
divergence of a mainline travel lane and an exit/entrance lane.

[2](a) A crash attenuator is a device intended to
reduce the damage to structures, vehicles, and motorists from a motor vehicle
collision by absorbing the colliding vehicle’s kinetic energy. (b) The Tesla’s restraint
control module was downloaded, and the speed at impact was recorded as 114
kilometers per hour (70.8 mph).

[3]Traffic-aware cruise control is an adaptive
cruise control system that allows a set speed and a set following distance from
a slower moving vehicle in front.​

Probable Cause

Probable Cause

​The information in
this preliminary report is subject to change and may contain errors.

It will be
supplemented or corrected during the course of the investigation.

No determination of probable cause is included in this preliminary report.